Device for mixing and/or injecting cements

ABSTRACT

The present invention relates to a device for storing and/or mixing and/or injecting cements, especially bone cements. The device includes a tube having a longitudinal axis, a front end with an outlet opening, a rear end; and an internal cylindrical cavity having a first end and a second end; a locking mechanism detachably connected to the front end of the tube so that the outlet opening can be sealed; and a lid detachably connected to the rear end of the tube; the lid having a borehole extending therethrough. The device also includes: a mixer having a mixing shaft sized and configured to extend through the borehole formed in the lid and a mixing tool at one end thereof, the mixer being axially and rotationally moveable inside of the cavity; a driving mechanism connected to the mixer shaft so that the mixer can be axially and rotationally moved with respect to the tube; and a first restraining mechanism for limiting the axial movement of the mixer with respect to the tube so that the a minimum distance A remains between the front face of the mixing tool and the front wall of the cavity; wherein the cylindrical cavity has a diameter D and the mixing tool has a maximum dimension X such that X is less than D.

Continuation of prior application No.: PCT/CH02/00204 filed Apr. 11,2002.

BACKGROUND OF THE INVENTION

The present invention relates to a device for storing and/or mixingand/or injecting cements, especially bone cements.

Many of the present-day cements, which are produced from two components,a powdery component and a liquid component, polymerize after thecomponents are mixed thoroughly and subsequently form a hard and more orless permanent cement composition. Aside from the polymerizable cements,so-called hydraulic cements, such as phosphate cements, may also beused.

Polymethacrylates, which are also referred to as PMMA, are mostfrequently used as bone cements at the present time. PMMA include apowdery polymer and a liquid monomer. When mixed, these componentspolymerize within minutes and form a firm connection between theprosthesis and the bone structure surrounding the prosthesis.

In addition, calcium phosphate cements are also increasingly used at thepresent time. Here also, a powdery component is mixed with a liquidcomponent. After the components are mixed, the cement is hardened by aprecipitation reaction.

Devices for mixing and metering pharmaceutical products are known. Forexample, German Patent No. DE 297 21 534 discloses a mixing and meteringcontainer which comprises a container body, which includes an internalcylindrical space having an outlet with a tapering diameter at one endand a piston unit at the other end of the container body. The pistonunit seals the end of the container body and is axially movable in theinternal cylindrical space. The piston unit has an opening for receivinga drive shaft of a mixing tool, which can be driven into the internalcylindrical space. The container also includes a driving device, whichengages the opening and is connected to the container body. However, thedriving device can only be connected to the container body after themixing tool is removed. The piston unit is moved by a threaded rod, thethreaded rod being actuated manually by an actuating element at the endof the driving device. It is a disadvantage of this known device that anadequate distance between the mixing tool and the wall of the mixingspace is not necessarily ensured so that, when abrasive powders aremixed, there may be appreciable wear on the mixing tool and/or on thewall of the mixing space, the abraded particles having a negative effecton the quality of the product.

SUMMARY OF THE INVENTION

The present invention attempts to provide a remedy for the disadvantagesassociated with the prior art. That is, it is an object of the inventionto provide a device for mixing a two-component cement, the deviceincluding restraining means for the mixing tool so that a minimumdistance is maintained between the mixing tool and the wall of themixing space thereby reducing abrasion on the mixing tool and/or on thewall of the mixing space.

The present invention may be used with different cements. In particular,the present invention is suitable for the preparation of so-called bonecements, which may be used for anchoring and supporting artificial jointcomponents and other prostheses.

Pursuant to the invention, this objective is accomplished with a devicefor storing, mixing, and/or injecting cements, especially bone cements,wherein the device includes a tube having a longitudinal axis, a frontend with an outlet opening, a rear end; and an internal cylindricalcavity, i.e., the mixing space, having a first end and a second end; alocking mechanism detachably connected to the front end of the tube sothat the outlet opening can be sealed; a lid detachably connected to therear end of the tube; the lid having a borehole extending therethrough;a mixer comprising a mixing shaft sized and configured to extend throughthe borehole formed in the lid and a mixing tool at the other endthereof, the mixer being axially and rotationally moveable inside of thecylindrical cavity; driving means connected to the mixer shaft so thatthe mixer can be axially and rotationally moved with respect to thetube; and first restraining means for limiting the axial movement of themixer with respect to the tube so that the a minimum distance A remainsbetween the front face of the mixing tool and the first end of thecavity; wherein the cylindrical cavity has a diameter D and the mixingtool has a maximum dimension X such that X is less than D.

The present device may also include a tube with an outlet opening at afront end thereof and a lid which can be detachably connected at a rearend thereof. The lid being detachably connected to the tube by a firstlocking means. The lid having a borehole, which is coaxial with thelongitudinal axis of the tube. The device also includes a mixer with amixing tool, which can be moved axially and rotationally in a cavityformed in the tube, and a mixing shaft, which passes through theborehole formed in the lid. The mixing shaft can be connected outside ofthe tube to a driving means in order to facilitate the axial androtational movement of the mixer. A locking mechanism may be detachablyconnected to the front end of the tube. The locking mechanism includesan axially continuous, central borehole, which is connected to theoutlet opening of the tube so that the central borehole and hence theoutlet opening can be closed off by a membrane. Thus, on the one hand,the outlet opening may be closed off by the membrane and, on the otherhand, the liquid component of the cement can be injected through themembrane without opening the device. Furthermore, the device may includerestraining means, by means of which the displacement of the mixing toolparallel to the longitudinal axis can be limited at least at the frontend of the tube.

In the preferred embodiment of the inventive device, the device includesa piston, which can be introduced into the cavity formed in the tubefrom the rear end of the tube. The piston being axially moveable withinthe cavity. The piston including a sealing lip concentric with thelongitudinal axis so that the front portion of the cavity, i.e., theportion in front of the piston, is sealed off from the rear portion ofthe cavity, i.e., the portion behind the piston. The piston alsoincludes a through hole extending therethrough coaxially with thelongitudinal axis so that the shaft of the mixer can be mounted throughthe through hole formed in the piston. Furthermore, the rear end of thetube can be closed off by a detachable a lid which includes a borehole,coaxial with the longitudinal axis of the cavity, so that the mixingshaft can also be passed through the borehole formed in the lid. Thedevice may also include restraining means configured so that the drivingmeans, when the mixing tool is in its position closets to the front endof the tube, comes to rest on what is regarded, with respect to thecavity, as the outside of the lid, so that a minimum distance A remainsbetween the mixing tool and the front cavity wall thereby forming anaxial boundary between the front face of the mixing tool and the firstend of the cavity. This minimum distance A preferably is between twiceand five times the diameter of the particles of the material beingmixed. For example, for bone cements, the diameter of the particles mayfall within the following ranges:

-   -   between 5 μm and 50 μm    -   between 50 μm and 800 μm or    -   between 5 μm and 800 μm.

Thus, the minimum distance A between the front face of the mixing tooland the front cavity wall may be:

-   -   10 μm and 250 μm, or between    -   100 μm and 4000 μm, or between    -   10 μm and 4000 μm.

Preferably, the cavity is coaxial with the longitudinal axis of the tubeand is cylindrically configured with a diameter D, when measuredperpendicular to the longitudinal axis. Preferably, the diameter D islarger than the maximum dimension X of the mixing tool, when measuredperpendicular to the longitudinal axis, the difference between thediameter D and the maximum dimension X (Δ=D−X) preferably being between4 times and 10 times the diameter of the largest particle of thematerial being mixed. Thus, in the various embodiments of the inventivedevice, this difference Δ may be between:

-   -   20 μm and 500 μm, or between    -   200 μm and 8000 μm, or between    -   20 μm and 8000 μm.

The diameter of the mixing shaft and the diameter of the through holeformed in the piston are such, that the mixing shaft has a slightclearance in the through hole so that movement of the mixer does notmove the piston during the mixing process.

In a different embodiment of the inventive device, the device mayinclude second restraining means, which are configured so that the axialdisplacement of the mixing tool is also limited towards the rear end ofthe tube so that the mixing tool, when it is in its position closest tothe rear end of the tube, is at a minimum distance B from the front facesurface of the piston, which is also pushed into its position closest tothe rear end of the tube. Preferably, the minimum distance B correspondsto the minimum distance A.

Because of (1) the distance A of the mixing tool from the front cavitywall, (2) the difference Δ of the mixing tool from the lateral cavitywall, and (3) the distance B of the mixing tool for the front facesurface of the piston, the present device ensures that there is no oronly very little wear on the cavity wall, the mixing tool and/or on thepiston during mixing of the abrasive particles. As previously stated,these distances should advantageously be more than twice the diameter ofthe particles.

In a further embodiment of the inventive device, the first restrainingmeans includes a first axial stop, mounted on the driving means. Thefirst axial stop preferably being constructed so that the driving meansis sized and configured to contact the lid, when the mixing tool is inits position closest to the first end of the cavity.

In yet another embodiment of the inventive device, the secondrestraining means includes a second axial stop, mounted on the mixingshaft and on the lid. The second axial stop preferably is constructed sothat the cross-sectional surface of the mixer shaft, orthogonal to thelongitudinal axis, is reduced in size at a distance L₁ from the frontend of the mixing tool and, complementary thereto, at a distance L₂ fromthe inner surface of the lid, the cross-sectional surface of theborehole formed in the lid, which is also orthogonal to the longitudinalaxis, is reduced in size. The distances L₁ and L₂ depend on the axialthickness of the mixing tool, the minimum distance B and the length ofthe piston.

Furthermore, the first locking means, which detachably connects the lidto the rear end of the tube, can be configured in various differentembodiments, such as a bayonet-type connection, a screw connection, asnap fit connection, etc.

Analogously to the first locking means, the second locking means, whichdetachably connects the locking mechanism to the front end of the tube,can also be configured in various different embodiments, such as abayonet-type connection, a screw connection, a snap fit connection, etc.

Moreover, the driving means for the axial and/or rotational movement ofthe mixer consists preferably of a handle. However, in other embodimentsof the inventive device, the driving means can be constructed as anelectrically, pneumatically or hydraulically working driving machine.

The present invention provides a device wherein none of the materialoriginating from the mixing container or the mixing tool reaches thematerial being mixed because of the distance between the mixing tool andthe mixing container. This is extremely important for implant materials,since particles of certain materials can lead to undesirable effects inthe body. Moreover, the powdery components of the cement can be storedin the inventive device and mixed with the liquid component at thedesired time. Subsequently, the mixture can be injected directly fromthe mixing space to the desired location. Thus, the present deviceensures that the material to be mixed is protected at all times from theenvironment and from possible contaminations therewith.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and further developments of the invention are described ineven greater detail in the following by means of the partiallydiagrammatic representations of several examples. In the drawing

FIG. 1 shows a longitudinal section through an embodiment of theinventive device, the mixer being in its position closest to the frontend of the tube and

FIG. 2 shows a longitudinal section through the embodiment of theinventive device, shown in FIG. 1, the mixer being in its positionclosest to the rear end of the tube.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an embodiment of the inventive device 1 with a tube 2 and amixer 14, which is shown in its position closest to the front end 3 ofthe tube 2. The tube 2 is configured with a hollow, cylindrical cavity 7which is concentric with the longitudinal axis 5. The cavity 7 having across sectional area Q extending orthogonal to the longitudinal axis 5.The mixer 14 is axially moveable along the longitudinal axis 5 of thetube 2 and can be rotated about the longitudinal axis 5. The tube 2includes a front cavity wall 20, which extends generally transverse tothe longitudinal axis 5, and a lateral wall 33, which extends generallyparallel to the longitudinal axis 5. The front end 3 of the tube 2 hasan outlet opening 6 with a cross-sectional area q extending orthogonalto the longitudinal axis 5. The cross-sectional area q of the outletopening is smaller than the cross-sectional area Q of the cavity 7.

The rear end 4 of the tube 2 includes a first locking means 29, which isdisposed on the external wall of the tube 2. The first locking means 29fastens a detachable lid 10 to the rear end 4 of the tube 2. In thepreferred embodiment of the inventive device 1 shown here, the firstlocking means 29 is configured as bayonet-type connection. Similarly,the front end 3 of the tube 2 may include a tubular attachment 31, whichis disposed coaxially with the longitudinal axis 5 and aligned with theoutlet opening 6. Second locking means 30 are disposed on the tubularattachment 31 so that a locking mechanism 12 can be detachably fastenedto the tubular attachment 31 so that the cavity 7 can be closed off,i.e., sealed, at the front end 3 of the tube 2. The locking mechanism 12may be pushed into the tubular attachment 31, coaxially along thelongitudinal axis 5, and up to the outlet opening 6. The lockingmechanism 12 has a central borehole 32, which is coaxial with thelongitudinal axis 5 and which can be closed off by means of a membrane13.

The device 1 may also include a piston 8, which is also axially moveablein the cavity 7 of the tube 2 along the longitudinal axis 5. As shown inFIG. 1, the piston 8 is in its rear position at the rear end 4 of thetube 2. The piston 8 serves to meter, ie., discharge, the mixedmaterial, which, as the piston 8 moves parallel to the longitudinal axis5 towards the front end 3 of the tube 2, emerges from the outlet opening6. The piston 8 also includes a through hole 9, which is coaxial withthe longitudinal axis 5 and which accommodates and guides the shaft 16of the mixer 14, i.e., the mixer shaft. The piston 8 may also include asealing lip 34, which is disposed concentrically with the longitudinalaxis 5 and by means of which the cavity 7 can be sealed off from therear end 4 of the tube 2.

As shown in FIG. 1, the lid 10 is detachably mounted at the rear end 4of the tube 2 and includes a borehole 11, which extends coaxially alongthe longitudinal axis 5 through the lid 10. The lid 10 may also furtherinclude a tube 24, which is coaxial with the longitudinal axis 5, andthrough which the borehole 11 coaxially passes so that the mixer shaft16 can be axially passed through the lid 10 and through the tube 24.

The mixer 14 may also include driving means 17 disposed at the rear end35 of the mixer shaft 16 axially opposite to the mixing tool 15. Asshown, the driving means 17 may be constructed as a handle. Aspreviously stated, the mixer 14 is axially and rotationally moveableinside of the cavity 7 and comprises a mixing tool 15 and a mixer shaft16, which can be passed through the through hole 9 formed in the piston8 and the borehole 11 formed in the lid 10 and in the tube 24. Themixing tool 15 is equipped with ports 19, which extend completelythrough the mixing tool 15 parallel to the longitudinal axis 5.

The device 1 may also include first restraining means 18, which limitthe axial displacement of the mixer 14 in the direction of the front end3 of the tube 2 in such a manner that, when the mixing tool 15 is in itsposition closest to the front end 3 of the tube 2, a minimum distance Aremains between the front face wall 41 of the mixing tool 15 and thefront wall 20 of the cavity 7. In this embodiment of the inventivedevice 1, the first restraining means 18 consists of a first axial stop21 wherein the front end 27 of the tubular continuation 26 of thedriving means 17 contacts the exterior surface of the lid 10 so that theminimum distance A between the front face wall 41 of the mixing tool 15and the front wall 20 of the cavity 7 is maintained. That is, the mixershaft 16 is connected to the driving means 17 in such a manner that alength L is maintained between the front end 40 of the mixing tool 15,which is directed towards the outlet opening 6, and the front end 27 ofthe tubular continuation 26 of the driving means 17. The length L beingdetermined by the length of the cavity 7 in the tube 2, the thickness ofthe lid 10 and the minimum distance A.

In FIG. 2, the mixing tool 15 and the piston 8 are in their positionclosest to the rear end 4 of the tube 2. The device 1 preferablyincludes a second restraining means 39, which limits the axialdisplacement of the mixer 14 with respect to the rear end 4 of the tube2. The second restraining means 39 includes a second axial stop 22,which, as shown, is configured as a first cross-sectional reduction insize 36 of the cross-sectional surface of the mixer shaft 16 and acomplementary second cross-sectional reduction in size 37 of thecross-sectional surface of the borehole 11. Through the inter-engagementof the second restraining means 39, it can be achieved that, when themixing tool 15 is in its position closest to the rear end 4 of the tube2, a minimum distance B remains between the rear face wall 42 of themixing tool 15 and the front face surface 23 of the piston 8. For thispurpose, the length L₁ between the front end 40 of the mixing tool 15and the first cross-sectional reduction in size 36 formed on the mixershaft 16 and the length L₂ between the inside surface of the lid 10,directed towards the cavity 7, and the second cross-sectional reductionin size 37 formed in the borehole 11 are dimensioned so that thedifference in lengths (L₁–L₂) corresponds to the sum of the axialdimensions of the mixing tool 15, the length of the piston 8 and theminimum distance B.

Furthermore, as seen perpendicularly to the longitudinal axis 5, themaximum dimension X of the mixing tool 15 is smaller than the diameter Dof the cavity 7 formed in the tube 2, orthogonal to the longitudinalaxis 5, so that the mixing tool 15 is at a distance from the side wall33 of the cavity.

At the end of the mixing process, after the lid 10 is loosened andretracted, the mixer shaft 16 can be broken off at a predeterminedbreaking point 38 so that the metering, i.e., discharging, of the cementby means of the piston 8 and a driving device (not shown) suitable forthis purpose is not impeded by the mixer shaft 16, the lid 10 or thedriving means 17. A manually operated rocker, such as that disclosed inEuropean Patent No. 0 326 551, for example, may be used as a drivingdevice. In use, the mixed cement is metered and discharged through theoutlet opening 6 by the piston 8 in the cavity 7. At the same time, themixing tool 15 is in a retracted position adjoining the front facesurface 23 of the piston 8 and is also moved by the piston 8.

1. A device for storing, mixing, and/or injecting cements, the devicecomprising: a tube having a longitudinal axis, a front end with anoutlet opening, a rear end; and an internal cylindrical cavity includinga first end with a front wall and a second end; a locking mechanismdetachably connected to the front end of the tube so that the outletopening can be sealed; a lid detachably connected to the rear end of thetube; the lid having a borehole extending therethrough; a mixer having amixing shaft sized and configured to extend through the borehole formedin the lid and a mixing tool at an end thereof, the mixing tool having afront face surface, the mixer being axially and rotationally moveableinside of the cavity; driving means connected to the mixer shaft so thatthe mixer can be axially and rotationally moved with respect to thetube; and first restraining means for limiting the axial movement of themixer with respect to the tube so that a minimum distance A remainsbetween the front face surface of the mixing tool and the front wall ofthe cavity; wherein the first restraining means comprises a first axialstop which is mounted on the driving means and which limits the axialdisplacement of the mixer with respect to the tube in the direction ofthe front end of the tube; wherein the cylindrical cavity has a diameterD and the mixing tool has a maximum dimension X such that X is less thanD.
 2. The device of claim 1, wherein the distance A is between 10 μm and4000 μm.
 3. The device of claim 2, wherein the distance A is between 25μm and 1600 μm.
 4. The device of claim 1, wherein the device furtherincludes a piston having a front face surface which is axiallydisplaceable in the cavity, parallel to the longitudinal axis, the frontface surface having a through hole extending therethrough so that themixer shaft can be passed through the through hole formed in the pistonand through the borehole formed in the lid; the device further includingsecond restraining means comprising an axial stop formed between themixer shaft and the borehole so that the axial movement of the mixer islimited when the mixer is moved in the direction of the rear end of thetube so that, when the piston and the mixing tool are in their positionclosest to the second end of the cavity, there is a minimum distance Bbetween the mixing tool and the front face surface of the piston.
 5. Thedevice of claim 4, wherein the distance B is between 10 μm and 4000 μm.6. The device of claim 5, wherein the distance B is between 25 μm and1600 μm.
 7. The device of claim 4, wherein the lid includes, parallel tothe longitudinal axis, a tube which extends towards the driving means,the tube having a borehole extending therethrough, and the axial stop ofthe second restraining means is formed by a reduction in size of thecross-sectional surface of the mixer shaft and a complementary reductionin size of the cross-sectional surface of the borehole.
 8. The device ofclaim 4, wherein the piston further includes a sealing lip, which isconcentric with the longitudinal axis.
 9. The device of claim 1, whereinthe driving means has a tubular continuation with a front end directedagainst the lid, the front end of the tubular continuation being at adistance L, measured parallel to the longitudinal axis, from the frontface surface of the mixing tool, the length L being dimensioned so thatthe front end of the tubular continuation contacts the lid when themixing tool is in its position closest to the first end of the cavity.10. The device of claim 1, wherein the difference between the diameter Dand the dimension X is between 20 μm and 8000 μm.
 11. The device ofclaim 10, wherein the difference between the diameter D and thedimension X, is between 50 μm and 3200 μm.
 12. The device of claim 1,wherein the lid is detachably connected to the tube by means of abayonet-type connection.
 13. The device of claim 12, wherein the pistonis moved by means of a driving device, which is detachably connected tothe tube by means of the bayonet type connection.
 14. The device ofclaim 1, wherein the front end of the tube further includes a tubularattachment, which is disposed coaxially with the outlet opening and thetubular attachment comprises a membrane for sealing off the outletopening.